Sex on the first date isn’t necessarily a bad thing, says a new book.Getty Images

Forget everything your mother and outdated guidebooks have told you — contrary to popular belief, it’s OK to put out on the first date.

Or so say Andrea Syrtash and Jeff Wilser, authors of the new dating tome appropriately named, “It’s Okay To Sleep with Him on the First Date: And Every Other Rule of Dating, Debunked.”

The NYC-based relationship specialists say the current crop of dating books are “of another era.”

“We don’t need graphs and matrices to figure out how to date,” bemoans Wilser. “People use these rules as a crutch.”

“You need to take risks in love,” adds Syrtash. “Some of the best stories I’ve heard about people who find love feature those who broke dating rules.”

Here’s a look at five dating rules to squash — and why:

1. Don’t sext.

There are some things you simply can’t prevent in the modern digital age — one of which is sexting. That said, Wilser warns: “If you haven’t actually slept with this person in real life, it’s too soon to sext.”

Their other rules for safe sexting include: Avoid abbreviations (“Hot4u” sounds anything but smoldering), make sure it’s someone you trust (a digital footprint is real . . . and dangerous) and try sexting while sober (a 10:30 a.m. sext is more provocative than a drunken one at 2:30 a.m.).

2. Never date a co-worker.

“We always hear that certain people are off-limits,” says Syrtash. “It’s hard to find chemistry and connections. Sometimes it shows up in places and packages you least expect.”

One of those places? The office — as long as good judgment is used. For one, keep your electronically transmitted hearts and kisses off company e-mail and IM. Don’t blab to the whole office. Figure out if it’s a fun hookup or if there’s long-term potential. And make sure office relations don’t explicitly violate company policy. . .then figure out if it’s worth losing your job over a crush.

3. Men love bitches, and nice guys finish last.

“This one really irks me,” says Wilser. “While there is something to the idea that men like the chase, this is taken to a cartoonish extreme.”

As Syrtash explains in the book, nice is not synonymous with boring or weak: “I’ve rarely heard anyone say, ‘I don’t like the person I’m dating because he’s thoughtful,’ or, ‘I don’t like her because she listens to what other people have to say and is caring.’ ”

4. Break it off if the sex is bad.

Although Syrtash says a lack of chemistry and passion can be a deal- breaker, she thinks new sexual partners should allow for an adjustment period before they pull the covers out from under them.

“So often we call sex bad when it’s just awkward and we haven’t found our rhythm yet,” she explains.

Wilser cautions, however, that it’s a fatal sign (which alcohol only solves temporarily) if you don’t desire the person or the thought of kissing them “gives you the willies.”

5. Never sleep with him on the first date.

Sure, there can be merit in waiting to sleep with a new amour, whether to build intrigue or because of religious beliefs.

The authors say just because a woman gives up her goodies, a guy isn’t going to deem her undateble.

“We don’t think, ‘This one’s girlfriend material because she waited a month, and that one’s booty-call material because she came back to my place,’ ” Wilser writes. “There mere act of waiting does not magically create chemistry. Waiting does not make us say, ‘Now, that’s the kind of woman I could marry!’ ”